An eco-hot water supply device has been provided as an example of a heat pump type hot water supply device (see Patent Document 1 and Patent Document 2).
As shown in FIG. 8, in this type of hot water supply device, a heat pump unit A on the side of a heat source includes a compressor 1, a heat radiating heat exchanger (condenser) 2, an expansion valve 3, and an air heat exchanger (evaporator) 4. The compressor 1 compresses refrigerant to obtain refrigerant of high temperature and high pressure. The heat radiating heat exchanger 2 condenses the refrigerant of high temperature and high pressure that is compressed by the compressor 1 to release heat from the refrigerant. The expansion valve 3 depressurizes the high-pressure refrigerant that is condensed by the heat radiating heat exchanger 2. The air heat exchanger 4 evaporates the refrigerant that is depressurized by the expansion valve 3 to absorb heat from air that is supplied via a fan 5.
A hot water supply unit B includes a water tank (hot water supply tank) 7, a water supply pipe 8, a water circulation pipe 9, and a heat absorbing heat exchanger (water side heat exchanger) 10. The water tank 7 stores water for supplying hot water. The water supply pipe 8 supplies water to a bottom section in the water tank 7. The water circulation pipe 9 extends from the bottom section to an upper section of the water tank 7 in a bypassing manner, and circulates the water in the water tank 7 from the bottom section to the upper section by a water pump 11. The heat absorbing heat exchanger 10 is arranged on the water circulation pipe 9 and connected to the heat radiating heat exchanger (refrigerant side heat exchanger) 2 of the heat pump unit A on the heat source side so as to absorb heat.
The heat source side heat pump unit A is combined with the hot water supply unit B to heat the water in the water tank 7 by the heat radiating heat exchanger 2 of the heat pump unit A on the heat source side via the heat absorbing heat exchanger 6 on the water circulation pipe 9 on the side of the hot water supply unit B.
In such a heat pump type hot water supply device, a constant amount of water is supplied to the water tank 7 from the water supply pipe 8 and stored in the water tank 7. Then, the water in the water tank 7 is heated up to a predetermined temperature (for example, 90° C.) intermittently by the heat radiating heat exchanger 2 of the heat pump unit A on the heat source side via the heat absorbing heat exchanger 10 provided on the water circulation pipe 9 on the side of the hot water supply unit B, and the heated hot water is stored in the upper section of the water tank 7. The hot water in the water tank 7 is discharged from the hot water supply pipe 12 to be used for a desired use such as for the bath, the kitchen, or the shower.
Therefore, in such a conventional heat pump type hot water supply device, a large amount of water is stored in the water tank 7 and the water in the water tank 7 is heated, and hot water is supplied as useful water (hot water). Therefore, the scale formed in the water tank 7 and the water circulation pipe 9 causes a problem.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2002-106963    Patent Document 2: Japanese Laid-Open Patent Publication No. 2003-83607